Acoustic wave interference produces audible effects observed and measured in archaeoacoustic research at the 3,000–year–old Andean Formative site at Chavín de Huántar, Perú. The ceremonial center’s highly–coupled network of labyrinthine interior spaces is riddled with resonances excited by the lower–frequency range of site–excavated conch shell horns. These pututus, when played together in near–unison tones, produce a distinct "beat" effect heard as the result of the amplitude variation that characterizes this linear interaction. Despite the straightforward acoustic explanation for this architecturally enhanced instrumental sound effect, the performative act reveals an intriguing perceptual complication. While playing pututus inside Chavín’s substantially intact stone–and–earthen–mortar buildings, pututu performers have reported an experience of having their instruments’ tones "guided" or "pulled" into tune with the dominant spatial resonances of particular locations. In an ancient ritual context, the recognition and understanding of such a sensory component would relate to a particular worldview beyond the reach of present–day investigators. Despite our temporal distance, an examination of the intertwined acoustic phenomena operative to this architectural–instrumental–experiential puzzle enriches the interdisciplinary research perspective, and substantiates perceptual claims.

Archaeoacoustics provides a channel through which experiential aspects of past human life might be accessed. Knowledge of physical dynamics, derived from the material remnants of past places, objects, and other artifacts of human actions, enables present-day evaluation of ephemera such as sound. Psychoacoustics, the science of sonic perception and cognition, can be employed in archaeological research to estimate human experiential implications of acoustic dynamics of environments, spaces, and objects. Experiential estimations may be made by applying findings from relevant experimental studies, or by conducting site-contextualized subjective experiments, either in situ where conditions permit testing, or in the lab using computational simulations known as auralizations. Although such sonic reconstructions are potentially useful as research tools and for knowledge sharing, as with any virtualization of reality, interpretative and presentational factors are problematically intertwined. Auralization might, therefore, be considered a mode of engagement with archaeological data. To illustrate theoretical concerns, methodologies, and applications, case-study examples are given here, based on data from acoustic measurements and auditory localization experiments conducted within the ceremonial architecture at the Andean Formative complex of Chavín de Huántar, Perú.

Ancient people are thought to have consulted an oracle at Chavín, yet until recently, few clues pointed to the nature of this oracle. Now, archaeoacoustic research--sonic science applied to archaeological evidence--has revealed secrets built into Chavín's architecture, unlocked by the sound of conch shells that were buried for millennia.

Essay for The Appendix: a new journal of narrative and experimental history.

Out Loud: Sound and Archaeology

Sound--because it's experiential--is an ephemeral artifact of spaces and objects that we can use to better understand past life. Scientific research techniques based on material evidence of the distant past give detail about the less apparent aspects of sound that are fundamental to human experience. Such findings permit reconstructions that can further illuminate elemental characteristics of ancient sound environments.

Integrative archaeoacoustics advances a methodology in which the physical dynamics of anthropogenic spaces and musical/sound-producing instruments are comparatively studied and anthropologically considered with respect to an archaeological context. Applied in ongoing research about the Andean Formative ceremonial center at Chavín de Huántar, Perú, this case study examines relationships among diverse forms of evidence from an ancient ritual setting while seeking relevant ethnographic data from present-day sources. Chavín's well-preserved architecture and site-excavated instruments (Strombus galeatus conch shell horns) allow direct acoustic testing and measurement, and provide material bases for perceptual evaluation by human participants in systematic studies. Site-contextualized psychoacoustic research, implemented via on-site auditory localization experiments and in progress for testing of virtual reconstructions, constitutes a methodical approach to the study of human experiential dynamics, a problematic and frequently neglected area in archaeological inquiry. Using this approach, we pose a framework for probing the interconnections among material culture, physical dynamic processes, sensory phenomena, and human experience, here applied in the investigation of sonified ritual in ancient Chavín.

Recent archaeoacoustics fieldwork at the 3,000-year-old Andean Formative Period ceremonial center at Chavín de Huántar, Peru has produced new physical dynamical evidence to characterize the site's ancient sound environment. We present findings from acoustic measurements of extant architecture, site-excavated sound-producing/musical instruments, and from tests performed on replica instruments in the exterior complex and its landscape setting. Our integrative methodology explores interrelationships among instrumental and environmental acoustics, and allows us to consider and test their human auditory perceptual implications. Results substantiate a new case for architectural acoustic use and design within a ritual framework.

Psychoacoustics is an experimental science that examines auditory perceptual and cognitive responses of living beings to sound. While established principles can inform research, systematic experimentation permits the site-contextualized evaluation of perception across a group of participants. Recent auditory localization experiments conducted within the Chavín galleries initiated in-situ human perceptual testing of interior architectural acoustic effects at the complex. Comparative analysis of measured acoustic data with psychoacoustic experimental evidence provides an empirical basis for reconstructing specific experiential dynamics at this Andean Formative ceremonial center. Findings support the premise of intentional and strategic manipulation of sensory experience at Chavín.

This study of ancient sound-producing instruments within a comprehensive archaeoacoustic investigation is greatly enhanced by an integrative methodology that explores interrelationships among instrumental and environmental acoustic dynamics, and considers their auditory perceptual implications. The 3000-year-old Andean Formative Period ceremonial center at Chavín de Huántar presents both Strombus galeatus marine shell horns known as pututus and well-preserved architecture, whose acoustics can be tested, measured, and computationally modeled. Comparative acoustic measurements of site instruments and architecture, further informed by on-site psychoacoustic experimentation, provide information about the auditory environment experienced by ritual participants in ancient Chavín. We present findings that demonstrate an architectural acoustic mechanism specifically linking the Chavín pututus to the area of the Lanzón Gallery and Circular Plaza, focal in this reputed oracle center. We propose a sounding oracle, and how it could be given voice.

Recent and ongoing archaeoacoustics fieldwork at the 3,000-year-old Andean Formative Period ceremonial center at Chavín de Huántar, Perú provides a framework for studying the acoustic dynamics of extant architecture, sound-producing instruments, and landforms. Examples from this comprehensive investigation at Chavín illustrate the application of acoustic principles, specification and use of equipment, and implementation of measurement and analysis techniques, via field methods including 1) spatial and instrumental acoustic impulse response measurements, 2) musical/sound-producing instrument performance and recording, 3) binaural recording, and 4) on-site auditory perceptual experiments with human participants. Our multidisciplinary approach advances comparative methods that integrate acoustic and psychoacoustic research with other archaeological data. Results illuminate plausible interrelationships between ancient sound environments and humans, and substantiate a new case for a sounding oracle at Chavín.

A group of 20 spectacularly decorated, playable Strombus galeatus marine shell trumpets or "pututus" were excavated in 2001 at the 3,000 year-old Formative Period ceremonial center at Chavín de Huántar, Perú, whose intact architecture gives these instruments plausible acoustic venues that can be studied today. We advance a methodology based on comparative acoustic measurements of site instruments and architecture, further informed by on-site psychoacoustic experimentation, to provide information about the auditory sensory environment experienced by ritual participants in ancient Chavín. Material evidence from this Andean site indicates foundational interest in sensory experience: iconography portrays transformed humans morphed with powerful animal forms; artifacts illustrate psychoactive plants, and include the tools used to process and ingest them; profoundly enclosed interior architecture is characterized by confined spaces connected by long corridors and staircases, which direct occupant movement through multi-level, maze-like constructions; numerous horizontal ducts interlace the complex and allow light manipulation; architectural features produce areas of strong acoustic resonance and modify sound level and quality. From this archaeological context, we present a comparative study of the acoustics of the Chavín pututus and architecture, showing how specific locations in the Chavín complex favor the frequency range and selected articulations of the pututus, which supports hypotheses regarding ritual use of site construction, as well as founds the difficult case for intention in acoustic design. This novel multidisciplinary research approach is extensible to other archaeological contexts.

A group of 20 spectacularly decorated, playable Strombus galeatus marine shell trumpets or "pututus" were excavated in 2001 at the 3,000 year-old Formative Period ceremonial center at Chavín de Huántar, Perú, whose intact architecture gives these instruments plausible acoustic venues that can be studied today. The cached location of the instruments, along with examples of site iconography depicting pututus, viewed with knowledge of shell trumpets across ancient and modern contexts, suggests their ritual importance and use potential; notably, the stylistic variety in iconography engraved on these pututus evinces diversity of identity, while their similarly worked forms and collocated resting place point to unity in ritual purpose. In this new work, we advance a methodology based on comparative acoustic measurements of site instruments and architecture, informed by on-site psychoacoustic experimentation, to provide information about the auditory sensory environment experienced by ritual participants in ancient Chavín. Material evidence from this Andean site indicates foundational interest in sensory experience: iconography portrays transformed humans morphed with powerful animal forms; artifacts illustrate psychoactive plants, and include the tools used to process and ingest them; profoundly enclosed interior architecture is characterized by confined spaces connected by long corridors and staircases, which direct occupant movement through multi-level, maze-like constructions; numerous horizontal ducts interlace the complex and allow light manipulation; architectural features produce areas of strong acoustic resonance and modify sound level and quality. From this context, we introduce a comparative study of the acoustics of the Chavín pututus and architecture, and present measurement-based hypotheses regarding the sonic components of ritual in an ancient ceremonial complex.

In 2001, twenty Strombus galeatus marine shell trumpets were excavated
at the 3,000 year-old ceremonial center at Chavín de Huántar, Perú, marking the first documented contextual discovery of intact sound-producing instruments at this Formative Period site in the Andean highlands. These playable shells are decorated and crafted for musical use with well-formed mouthpieces created by cutting the small end (spire) off and grinding/polishing the resulting opening. The shells are use-polished, and additionally modified with a v-shaped cut to the outer apical lip. We present an acoustic analysis of the measured response of each instrument, to a variety
of excitations, at microphones placed in the mouthpiece, player's mouth, bore, bell, and surrounding near-field. From these measurements we characterize each
instrument's sounding frequencies (fundamental and 1st overtone where possible),
radiation pattern, and impedance, and we estimate the bore area function of each
shell. Knowledge of the specific acoustic capabilities of these pututus allows us to understand and test their potential as sound sources in the ancient Chavín context, whose architectural acoustics are simultaneously studied by our research group.

Inspired by on-site observations and measurements, a computational acoustic model of the interior architecture of the 3,000 year-old ceremonial center at Chavín de Huántar, Perú is presented. The model addresses the foundational study by Lumbreras, González and Lietaer (1976) which posited an acoustic system integral to Chavín architecture involving "a network of resonance rooms connected by sound transmission tubes". We propose a translation of the topology of Chavín gallery forms to a modular computational acoustic model based on bi-directional digital waveguides, representing the corridors and ducts, connected through reverberant scattering junctions, representing the small rooms. This approach combines known architectural dimensional and material data with representative measured acoustic data, thus economizing the collection of impulse response measurements required to accurately simulate site acoustics. Applications include virtual acoustic reconstruction of inaccessible or demolished site structures, and auralizations of hypothesized architectural forms, allowing any desired sound sample to be "played back" in the modeled acoustic context.

There are many impulse response measurement scenarios in which the playback and recording devices maintain separate unsynchronized digital clocks resulting in clock drift. Clock drift is problematic for impulse response measurement techniques involving convolution, including sinusoidal sweeps and pseudo-random noise sequences. We present analysis of both a drifting record clock and playback clock, with a focus on swept sinusoids. When using a sinusoidal sweep without accounting for clock drift, the resulting impulse response is seen to be convolved with an allpass filter having the same frequency trajectory form as the input swept sinusoid with a duration proportional to the input sweep length. Two methods are proposed for estimating the clock drift and compensating for its effects in producing an impulse response measurement. Both methods are shown to effectively eliminate any clock effects in producing room impulse response measurements.

An acoustically transparent, configurable microphone array with omnidirectional elements, designed for room acoustics analysis and synthesis, and archaeological acoustics applications, is presented. Omnidirectional microphone elements with 2 mm-diameter capsules and 1 mm-diameter wire mounts produce a nearly acoustically transparent array, and provide a simplified mathematical framework for processing measured signals. The wire mounts are fitted onto a 1.6 cm-diameter tube forming the microphone stand, with the microphones arranged above the tube so that acoustic energy can propagate freely across the array. The wire microphone mounts have some flexibility, and the array may be configured. Detachable arms with small speakers are used to estimate the element positions with an accuracy better than the 2 mm microphone diameter.

The archaeological record provides evidence for the pivotal role of Chavín de Huántar in the Andean evolution of social inequality, in part via legitimization of authority through sensory manipulation. To understand auditory implications of site design, we are measuring, quantifying, and archiving extant acoustics, and creating computer models to enable comprehensive objective evaluation. Preliminary studies confirm that architectural features of galleries at Chavín create acoustic conditions that obscure auditory localization cues. Such indications of structure-based auditory disorientation are consistent with sensory manipulation being a factor in design, and ground inferences regarding the contextual potential of the Chavín Strombus trumpets.

Chavín de Huántar is a monumental World Heritage archaeological site in the Peruvian highlands, predating Inca society by over 2000 years. The importance of site acoustics is suggested by distinctive architectural features,
notably an extensive network of underground galleries used in part for ritual purposes. The labyrinthine galleries are stone-walled and arranged in a series of small rectangular alcoves off narrow corridors. In this work, we initiate research that seeks to understand how the acoustics at Chavín may have influenced auditory experience.

Acoustic measurements and models of a site can be used to archive site acoustics, estimate the acoustics of inaccessible or alternative site architectures, and reconstruct the acoustics of modified or damaged sectors; they may also corroborate aspects of rituals suggested by other archaeological data. Preliminary measurements at Chavín show a short reverberation time, dense and energetic early reflections, and low inter-aural cross correlation. The short reverberation time would enable rhythmically articulated playing of Strombus shell trumpets found on site. The early reflection patterns would provide strong acoustic reinforcement and resonances in gallery alcoves. The wide soundfields would provide a sense of spaciousness and envelopment, contributing to ritual experience.